Re: Tac-nukes vs. Nuclear Warheads
There's a qualitative as well as quantitative difference.
Most tactical level devices are pure fission or deuterium-enhanced fission; they're not much worse than the effects we can get with modern conventional munitions, such as Daisy-Cutter Fuel-Air Explosives (in fact, this is one reason Daisy-Cutters are used sparingly - they can be confused with a low-yield nuke).
Strategic devices, whether single-warhead, multiple warhead or true MIRV (Multiple Independent Reentry Vehicles - individual warheads that each have a separate target and home individually) are usually fusion weapons. That gives between five and ten times the yield of a same-size fission device.
20d6 Armour Piercing, Penetrating, Explosive, reduced dropoff (1 dice per five hexes) is what I'd use for a Tactical weapon - while small, they are astonishingly lethal, and nothing but the most powerful supers should be able to survive being close to one.
For a small Strategic weapon, make it more like 30d6, double armour piercing, penetrating, explosion megascale 1KM for a 1 megaton device; scale up according to the megatonnage. Note that with multiple-warhead devices, they're designed to detonate in a radius around the actual target, massively enhancing the footprint.